/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:		arm_conv_q31.c
*
* Description:	Convolution of Q31 sequences.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.11 2011/10/18
*    Bug Fix in conv, correlation, partial convolution.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated
*
* Version 0.0.7  2010/06/10
*    Misra-C changes done
*
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup Conv
 * @{
 */

/**
 * @brief Convolution of Q31 sequences.
 * @param[in] *pSrcA points to the first input sequence.
 * @param[in] srcALen length of the first input sequence.
 * @param[in] *pSrcB points to the second input sequence.
 * @param[in] srcBLen length of the second input sequence.
 * @param[out] *pDst points to the location where the output result is written.  Length srcALen+srcBLen-1.
 * @return none.
 *
 * @details
 * <b>Scaling and Overflow Behavior:</b>
 *
 * \par
 * The function is implemented using an internal 64-bit accumulator.
 * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
 * There is no saturation on intermediate additions.
 * Thus, if the accumulator overflows it wraps around and distorts the result.
 * The input signals should be scaled down to avoid intermediate overflows.
 * Scale down the inputs by log2(min(srcALen, srcBLen)) (log2 is read as log to the base 2) times to avoid overflows,
 * as maximum of min(srcALen, srcBLen) number of additions are carried internally.
 * The 2.62 accumulator is right shifted by 31 bits and saturated to 1.31 format to yield the final result.
 *
 * \par
 * See <code>arm_conv_fast_q31()</code> for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4.
 */

void arm_conv_q31(
    q31_t* pSrcA,
    uint32_t srcALen,
    q31_t* pSrcB,
    uint32_t srcBLen,
    q31_t* pDst)
{


#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	q31_t* pIn1;                                   /* inputA pointer */
	q31_t* pIn2;                                   /* inputB pointer */
	q31_t* pOut = pDst;                            /* output pointer */
	q31_t* px;                                     /* Intermediate inputA pointer  */
	q31_t* py;                                     /* Intermediate inputB pointer  */
	q31_t* pSrc1, *pSrc2;                          /* Intermediate pointers */
	q63_t sum;                                     /* Accumulator */
	q63_t acc0, acc1, acc2;                        /* Accumulator */
	q31_t x0, x1, x2, c0;                          /* Temporary variables to hold state and coefficient values */
	uint32_t j, k, count, blkCnt, blockSize1, blockSize2, blockSize3;     /* loop counter */

	/* The algorithm implementation is based on the lengths of the inputs. */
	/* srcB is always made to slide across srcA. */
	/* So srcBLen is always considered as shorter or equal to srcALen */
	if(srcALen >= srcBLen) {
		/* Initialization of inputA pointer */
		pIn1 = pSrcA;

		/* Initialization of inputB pointer */
		pIn2 = pSrcB;
	} else {
		/* Initialization of inputA pointer */
		pIn1 = (q31_t*) pSrcB;

		/* Initialization of inputB pointer */
		pIn2 = (q31_t*) pSrcA;

		/* srcBLen is always considered as shorter or equal to srcALen */
		j = srcBLen;
		srcBLen = srcALen;
		srcALen = j;
	}

	/* conv(x,y) at n = x[n] * y[0] + x[n-1] * y[1] + x[n-2] * y[2] + ...+ x[n-N+1] * y[N -1] */
	/* The function is internally
	 * divided into three stages according to the number of multiplications that has to be
	 * taken place between inputA samples and inputB samples. In the first stage of the
	 * algorithm, the multiplications increase by one for every iteration.
	 * In the second stage of the algorithm, srcBLen number of multiplications are done.
	 * In the third stage of the algorithm, the multiplications decrease by one
	 * for every iteration. */

	/* The algorithm is implemented in three stages.
	   The loop counters of each stage is initiated here. */
	blockSize1 = srcBLen - 1u;
	blockSize2 = srcALen - (srcBLen - 1u);
	blockSize3 = blockSize1;

	/* --------------------------
	 * Initializations of stage1
	 * -------------------------*/

	/* sum = x[0] * y[0]
	 * sum = x[0] * y[1] + x[1] * y[0]
	 * ....
	 * sum = x[0] * y[srcBlen - 1] + x[1] * y[srcBlen - 2] +...+ x[srcBLen - 1] * y[0]
	 */

	/* In this stage the MAC operations are increased by 1 for every iteration.
	   The count variable holds the number of MAC operations performed */
	count = 1u;

	/* Working pointer of inputA */
	px = pIn1;

	/* Working pointer of inputB */
	py = pIn2;


	/* ------------------------
	 * Stage1 process
	 * ----------------------*/

	/* The first stage starts here */
	while(blockSize1 > 0u) {
		/* Accumulator is made zero for every iteration */
		sum = 0;

		/* Apply loop unrolling and compute 4 MACs simultaneously. */
		k = count >> 2u;

		/* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
		 ** a second loop below computes MACs for the remaining 1 to 3 samples. */
		while(k > 0u) {
			/* x[0] * y[srcBLen - 1] */
			sum += (q63_t) * px++ * (*py--);
			/* x[1] * y[srcBLen - 2] */
			sum += (q63_t) * px++ * (*py--);
			/* x[2] * y[srcBLen - 3] */
			sum += (q63_t) * px++ * (*py--);
			/* x[3] * y[srcBLen - 4] */
			sum += (q63_t) * px++ * (*py--);

			/* Decrement the loop counter */
			k--;
		}

		/* If the count is not a multiple of 4, compute any remaining MACs here.
		 ** No loop unrolling is used. */
		k = count % 0x4u;

		while(k > 0u) {
			/* Perform the multiply-accumulate */
			sum += (q63_t) * px++ * (*py--);

			/* Decrement the loop counter */
			k--;
		}

		/* Store the result in the accumulator in the destination buffer. */
		*pOut++ = (q31_t)(sum >> 31);

		/* Update the inputA and inputB pointers for next MAC calculation */
		py = pIn2 + count;
		px = pIn1;

		/* Increment the MAC count */
		count++;

		/* Decrement the loop counter */
		blockSize1--;
	}

	/* --------------------------
	 * Initializations of stage2
	 * ------------------------*/

	/* sum = x[0] * y[srcBLen-1] + x[1] * y[srcBLen-2] +...+ x[srcBLen-1] * y[0]
	 * sum = x[1] * y[srcBLen-1] + x[2] * y[srcBLen-2] +...+ x[srcBLen] * y[0]
	 * ....
	 * sum = x[srcALen-srcBLen-2] * y[srcBLen-1] + x[srcALen] * y[srcBLen-2] +...+ x[srcALen-1] * y[0]
	 */

	/* Working pointer of inputA */
	px = pIn1;

	/* Working pointer of inputB */
	pSrc2 = pIn2 + (srcBLen - 1u);
	py = pSrc2;

	/* count is index by which the pointer pIn1 to be incremented */
	count = 0u;

	/* -------------------
	 * Stage2 process
	 * ------------------*/

	/* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
	 * So, to loop unroll over blockSize2,
	 * srcBLen should be greater than or equal to 4 */
	if(srcBLen >= 4u) {
		/* Loop unroll by 3 */
		blkCnt = blockSize2 / 3;

		while(blkCnt > 0u) {
			/* Set all accumulators to zero */
			acc0 = 0;
			acc1 = 0;
			acc2 = 0;

			/* read x[0], x[1], x[2] samples */
			x0 = *(px++);
			x1 = *(px++);

			/* Apply loop unrolling and compute 3 MACs simultaneously. */
			k = srcBLen / 3;

			/* First part of the processing with loop unrolling.  Compute 3 MACs at a time.
			 ** a second loop below computes MACs for the remaining 1 to 2 samples. */
			do {
				/* Read y[srcBLen - 1] sample */
				c0 = *(py);

				/* Read x[3] sample */
				x2 = *(px);

				/* Perform the multiply-accumulates */
				/* acc0 +=  x[0] * y[srcBLen - 1] */
				acc0 += ((q63_t) x0 * c0);
				/* acc1 +=  x[1] * y[srcBLen - 1] */
				acc1 += ((q63_t) x1 * c0);
				/* acc2 +=  x[2] * y[srcBLen - 1] */
				acc2 += ((q63_t) x2 * c0);

				/* Read y[srcBLen - 2] sample */
				c0 = *(py - 1u);

				/* Read x[4] sample */
				x0 = *(px + 1u);

				/* Perform the multiply-accumulate */
				/* acc0 +=  x[1] * y[srcBLen - 2] */
				acc0 += ((q63_t) x1 * c0);
				/* acc1 +=  x[2] * y[srcBLen - 2] */
				acc1 += ((q63_t) x2 * c0);
				/* acc2 +=  x[3] * y[srcBLen - 2] */
				acc2 += ((q63_t) x0 * c0);

				/* Read y[srcBLen - 3] sample */
				c0 = *(py - 2u);

				/* Read x[5] sample */
				x1 = *(px + 2u);

				/* Perform the multiply-accumulates */
				/* acc0 +=  x[2] * y[srcBLen - 3] */
				acc0 += ((q63_t) x2 * c0);
				/* acc1 +=  x[3] * y[srcBLen - 2] */
				acc1 += ((q63_t) x0 * c0);
				/* acc2 +=  x[4] * y[srcBLen - 2] */
				acc2 += ((q63_t) x1 * c0);

				/* update scratch pointers */
				px += 3u;
				py -= 3u;

			} while(--k);

			/* If the srcBLen is not a multiple of 3, compute any remaining MACs here.
			 ** No loop unrolling is used. */
			k = srcBLen - (3 * (srcBLen / 3));

			while(k > 0u) {
				/* Read y[srcBLen - 5] sample */
				c0 = *(py--);

				/* Read x[7] sample */
				x2 = *(px++);

				/* Perform the multiply-accumulates */
				/* acc0 +=  x[4] * y[srcBLen - 5] */
				acc0 += ((q63_t) x0 * c0);
				/* acc1 +=  x[5] * y[srcBLen - 5] */
				acc1 += ((q63_t) x1 * c0);
				/* acc2 +=  x[6] * y[srcBLen - 5] */
				acc2 += ((q63_t) x2 * c0);

				/* Reuse the present samples for the next MAC */
				x0 = x1;
				x1 = x2;

				/* Decrement the loop counter */
				k--;
			}

			/* Store the results in the accumulators in the destination buffer. */
			*pOut++ = (q31_t)(acc0 >> 31);
			*pOut++ = (q31_t)(acc1 >> 31);
			*pOut++ = (q31_t)(acc2 >> 31);

			/* Increment the pointer pIn1 index, count by 3 */
			count += 3u;

			/* Update the inputA and inputB pointers for next MAC calculation */
			px = pIn1 + count;
			py = pSrc2;

			/* Decrement the loop counter */
			blkCnt--;
		}

		/* If the blockSize2 is not a multiple of 3, compute any remaining output samples here.
		 ** No loop unrolling is used. */
		blkCnt = blockSize2 - 3 * (blockSize2 / 3);

		while(blkCnt > 0u) {
			/* Accumulator is made zero for every iteration */
			sum = 0;

			/* Apply loop unrolling and compute 4 MACs simultaneously. */
			k = srcBLen >> 2u;

			/* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
			 ** a second loop below computes MACs for the remaining 1 to 3 samples. */
			while(k > 0u) {
				/* Perform the multiply-accumulates */
				sum += (q63_t) * px++ * (*py--);
				sum += (q63_t) * px++ * (*py--);
				sum += (q63_t) * px++ * (*py--);
				sum += (q63_t) * px++ * (*py--);

				/* Decrement the loop counter */
				k--;
			}

			/* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
			 ** No loop unrolling is used. */
			k = srcBLen % 0x4u;

			while(k > 0u) {
				/* Perform the multiply-accumulate */
				sum += (q63_t) * px++ * (*py--);

				/* Decrement the loop counter */
				k--;
			}

			/* Store the result in the accumulator in the destination buffer. */
			*pOut++ = (q31_t)(sum >> 31);

			/* Increment the MAC count */
			count++;

			/* Update the inputA and inputB pointers for next MAC calculation */
			px = pIn1 + count;
			py = pSrc2;

			/* Decrement the loop counter */
			blkCnt--;
		}
	} else {
		/* If the srcBLen is not a multiple of 4,
		 * the blockSize2 loop cannot be unrolled by 4 */
		blkCnt = blockSize2;

		while(blkCnt > 0u) {
			/* Accumulator is made zero for every iteration */
			sum = 0;

			/* srcBLen number of MACS should be performed */
			k = srcBLen;

			while(k > 0u) {
				/* Perform the multiply-accumulate */
				sum += (q63_t) * px++ * (*py--);

				/* Decrement the loop counter */
				k--;
			}

			/* Store the result in the accumulator in the destination buffer. */
			*pOut++ = (q31_t)(sum >> 31);

			/* Increment the MAC count */
			count++;

			/* Update the inputA and inputB pointers for next MAC calculation */
			px = pIn1 + count;
			py = pSrc2;

			/* Decrement the loop counter */
			blkCnt--;
		}
	}


	/* --------------------------
	 * Initializations of stage3
	 * -------------------------*/

	/* sum += x[srcALen-srcBLen+1] * y[srcBLen-1] + x[srcALen-srcBLen+2] * y[srcBLen-2] +...+ x[srcALen-1] * y[1]
	 * sum += x[srcALen-srcBLen+2] * y[srcBLen-1] + x[srcALen-srcBLen+3] * y[srcBLen-2] +...+ x[srcALen-1] * y[2]
	 * ....
	 * sum +=  x[srcALen-2] * y[srcBLen-1] + x[srcALen-1] * y[srcBLen-2]
	 * sum +=  x[srcALen-1] * y[srcBLen-1]
	 */

	/* In this stage the MAC operations are decreased by 1 for every iteration.
	   The blockSize3 variable holds the number of MAC operations performed */

	/* Working pointer of inputA */
	pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
	px = pSrc1;

	/* Working pointer of inputB */
	pSrc2 = pIn2 + (srcBLen - 1u);
	py = pSrc2;

	/* -------------------
	 * Stage3 process
	 * ------------------*/

	while(blockSize3 > 0u) {
		/* Accumulator is made zero for every iteration */
		sum = 0;

		/* Apply loop unrolling and compute 4 MACs simultaneously. */
		k = blockSize3 >> 2u;

		/* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
		 ** a second loop below computes MACs for the remaining 1 to 3 samples. */
		while(k > 0u) {
			/* sum += x[srcALen - srcBLen + 1] * y[srcBLen - 1] */
			sum += (q63_t) * px++ * (*py--);
			/* sum += x[srcALen - srcBLen + 2] * y[srcBLen - 2] */
			sum += (q63_t) * px++ * (*py--);
			/* sum += x[srcALen - srcBLen + 3] * y[srcBLen - 3] */
			sum += (q63_t) * px++ * (*py--);
			/* sum += x[srcALen - srcBLen + 4] * y[srcBLen - 4] */
			sum += (q63_t) * px++ * (*py--);

			/* Decrement the loop counter */
			k--;
		}

		/* If the blockSize3 is not a multiple of 4, compute any remaining MACs here.
		 ** No loop unrolling is used. */
		k = blockSize3 % 0x4u;

		while(k > 0u) {
			/* Perform the multiply-accumulate */
			sum += (q63_t) * px++ * (*py--);

			/* Decrement the loop counter */
			k--;
		}

		/* Store the result in the accumulator in the destination buffer. */
		*pOut++ = (q31_t)(sum >> 31);

		/* Update the inputA and inputB pointers for next MAC calculation */
		px = ++pSrc1;
		py = pSrc2;

		/* Decrement the loop counter */
		blockSize3--;
	}

#else

	/* Run the below code for Cortex-M0 */

	q31_t* pIn1 = pSrcA;                           /* input pointer */
	q31_t* pIn2 = pSrcB;                           /* coefficient pointer */
	q63_t sum;                                     /* Accumulator */
	uint32_t i, j;                                 /* loop counter */

	/* Loop to calculate output of convolution for output length number of times */
	for(i = 0; i < (srcALen + srcBLen - 1); i++) {
		/* Initialize sum with zero to carry on MAC operations */
		sum = 0;

		/* Loop to perform MAC operations according to convolution equation */
		for(j = 0; j <= i; j++) {
			/* Check the array limitations */
			if(((i - j) < srcBLen) && (j < srcALen)) {
				/* z[i] += x[i-j] * y[j] */
				sum += ((q63_t) pIn1[j] * (pIn2[i - j]));
			}
		}

		/* Store the output in the destination buffer */
		pDst[i] = (q31_t)(sum >> 31u);
	}

#endif /*     #ifndef ARM_MATH_CM0 */

}

/**
 * @} end of Conv group
 */
